The present application relates to an optical element, an optical device, and a method of producing an optical element.
Recently, demands for optical elements such as liquid crystal display elements, and optical devices have markedly increased. In such optical elements and optical devices, for example, in order to increase the transmittance of light, to prevent reflection of light, and to protect the surface of a display element, an optical film including a silicon oxide sublayer, a tin oxide sublayer, and the like is provided on a substrate made of a plastic or the like, and this substrate made of a plastic or the like with the optical film provided thereon is bonded onto the display element.
Such an optical film is provided on a substrate of an optical element or an optical device as a plurality of sublayers having different refractive indices in order to mainly prevent the reflection of external light. However, the adhesiveness, the durability, and the like of the bond between the substrate, in particular, a plastic substrate, and the optical film that are used in the optical element or the optical device are not satisfactory. Consequently, in an optical element such as a liquid crystal display element or an optical device, in order to improve the adhesiveness between the optical film, which is made of inorganic substances, and the plastic substrate, which is made of an organic substance, for example, a thin film made of titanium or chromium, or a thin layer made of an oxide such as silicon monoxide (SiO) or silicon dioxide (SiO2) is provided. Such a thin film provided between the optical film and the plastic substrate is referred to as a close-contact layer, an adhesive layer, an interlayer, or the like.
Japanese Unexamined Patent Application Publication No. 2003-94548 ('548 document) entitled “anti-reflection film” (FIG. 1, paragraphs 0014 and 0015 and paragraphs 0017 to 0019) discloses an anti-reflection film described below.
FIG. 8A, which is FIG. 1 in '548 document, is a view showing an example of the structure of an anti-reflection film including an adhesive layer.
FIG. 8A shows a lamination structure of an anti-reflection film according to an embodiment of '548 document. The anti-reflection film includes a substrate 41, an adhesive layer 43 for improving the adhesiveness provided on the substrate 41, an anti-reflection layer 40 provided on the adhesive layer 43, and an antifouling sublayer 33 provided on the anti-reflection layer 40. The anti-reflection layer 40 includes an alloy oxide sublayer 45 functioning as a medium-refractive-index sublayer, a high-refractive-index sublayer 47, and a low-refractive-index sublayer 49.
In the above structure, the substrate 41 is made of a film having high transparency in the visible light range, such as a film of an alicyclic polyolefin, e.g., polyethylene terephthalate (PET) or polycarbonate (PC), or triacetyl cellulose (TAC). However, the material of the substrate 41 is not limited to an organic substance, and the substrate 41 may be made of an inorganic substance.
The adhesive layer 43 is made of at least one material selected from Si, SiOx (wherein x=1 to 2), SiN, SiOxNy (wherein x=1 to 2 and y=0.2 to 0.6), CrOx (wherein x=0.2 to 1.5), and ZrOx (wherein x=1 to 2) and deposited by, for example, an AC sputtering method. The adhesive layer 43 has a thickness in the range of about 3 to 5 nm, which is sufficiently smaller than the wavelength of light. Therefore, this layer does not affect optical characteristics of the anti-reflection film.
The anti-reflection layer 40 provided on the substrate 41, with the adhesive layer 43 therebetween, is formed by sequentially depositing each sublayer by a reactive sputtering method. The alloy oxide sublayer 45 is deposited first as a medium-refractive-index sublayer. The alloy oxide sublayer 45 is made of an alloy oxide material containing Si: Sn, Zr, Ti, Ta, Sb, In, or Nb; and oxygen, which forms an oxide thereof. The refractive index of this alloy oxide sublayer 45 can be controlled by changing the component ratio in the alloy and is optimized in accordance with the refractive index of the substrate 41.
The high-refractive-index sublayer 47 provided on the alloy oxide sublayer 45 is made of a material such as TiO2, Nb2O5, SiN, Ta2O5, ITO, IZO, GZO, or AZO. The low-refractive-index sublayer 49 provided on the high-refractive-index sublayer 47 is made of a material such as SiO2 or MgF2.
The antifouling sublayer 33 provided on the low-refractive-index sublayer 49 is made of, for example, an alkoxysilane compound having a perfluoropolyether group and formed by a wet process.
According to the above structure, the refractive index of the medium-refractive-index sublayer can be easily optimized in accordance with the refractive index of the substrate 41. A three-layered anti-reflection (AR) film having excellent anti-reflection performance can be easily produced, and an anti-reflection film having excellent durability and antifouling property can be obtained.
PCT Japanese Translation Patent Publication No. 2005-502077 ('077 document) entitled “anti-reflection film and method related thereto” (FIG. 1, paragraphs 0010 to 0016) discloses an anti-reflection film described below.
FIG. 8B, which is FIG. 1 in '077 document, is a view showing an example of the structure of an anti-reflection film that does not include an adhesive layer.
The anti-reflection film shown in FIG. 8B is deposited on a substrate 53 used as a base described in an embodiment of '077 document. This substrate 53 is made of glass or a plastic. An optical thin film 51 includes a first sublayer 55, a second sublayer 57, and a third sublayer 59. The first sublayer 55 is deposited on the substrate 53, the second sublayer 57 is deposited on the first sublayer 55, and the third sublayer 59 is deposited on the second sublayer 57. These depositions are performed by sputtering, evaporation by heating, or another method of the related art. The first sublayer 55 has a medium refractive index, for example, in the range of about 1.7 to 2.1.The second sublayer 57 has a high refractive index, for example, in the range of about 2.2 to 2.6.The third sublayer 59 has a low refractive index, for example, in the range of about 1.46 to 1.52.
The first sublayer 55 is made of a dielectric material such as silicon nitride, zinc oxide, indium tin oxide (ITO), bismuth oxide, stannic oxide, zirconium oxide, hafnium oxide, antimony oxide, or gadolinium oxide. The second sublayer 57 is made of titanium oxide, niobium oxide, or tantalum oxide. Titanium oxide has a refractive index of about 2.4 or more, niobium oxide has a refractive index of about 2.28,and tantalum oxide has a refractive index of about 2.2.The third sublayer 59 is made of silicon oxide or magnesium fluoride.
Apparatuses for forming thin films are disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2003-114302 (FIG. 2, paragraphs 0022 to 0024), Japanese Unexamined Patent Application Publication No. 2001-116921 (FIG. 2,paragraphs 0015 to 0023), and Japanese Unexamined Patent Application Publication No. 10-48402 (FIGS. 3 to 6,paragraphs 0031 to 0048).
A metallic mode and an oxide mode in reactive sputtering are disclosed in, for example, Japanese Unexamined Patent Application Publication No. 10-30177 (FIG. 1,paragraphs 0009 to 0013). Japanese Unexamined Patent Application Publication No. 2006-284453 ('453 document) entitled “method of evaluating thin-film adhesiveness” discloses the following method (FIGS. 1 and 2,paragraphs 0009 to 0013).
As described therein, the '453 document relates to a method of evaluating the thin-film adhesiveness for quantitatively evaluating the adhesiveness between a thin film deposited on a plastic substrate and the substrate. In the method, a diamond indenter is pressed into a thin film, while a certain amount of load is applied to the indenter. Thus, an indentation depth-load curve characteristic is measured. A displacement point at which the deformation of the film is changed from elastic deformation to plastic deformation in the resulting indentation depth-load curve characteristic is defined as a separation point. A value obtained by multiplying the indentation depth from the starting point to the above separation point by the load applied from the starting point to the above separation point is defined as a workload, and the integrated value from the starting point to the separation point is used as an indicator of the adhesion strength between the thin film and the substrate.
In the method of evaluating the thin-film adhesiveness disclosed in '453 document, more specifically, the indentation depth-load curve characteristic is measured by pressing a triangular pyramid-shaped diamond indenter having a small radius of curvature and a sharp end into a thin film using a TriboIndenter.
Furthermore, in the method of evaluating the thin-film adhesiveness disclosed in '453 document, the adhesiveness between a plastic substrate and a thin film made of an inorganic material and deposited on the substrate is quantitatively evaluated. In the '453 document, by using a vertical indentation, the adhesive force between an ultra thin film having a nanometer-order thickness, for example, a thickness of about several tens of nanometers, and a substrate can be quantitatively measured with a high repeatability. Accordingly, the adhesive force of a thin film having a nanometer-order thickness can be quantitatively evaluated with a high repeatability.
In the related art, an adhesive layer is provided between a substrate (support) such as a plastic film and an anti-reflection layer. However, when the anti-reflection layer is formed on a substrate such as a flexible plastic film, the anti-reflection layer is easily separated from the substrate. For example, in an anti-reflection film produced by forming a SiOx (wherein 1<x<2) film serving as an adhesive layer on a PET film used as a substrate, and forming a SnO2 thin film serving as the bottom sublayer of the anti-reflection layer on the adhesive layer, cracks are formed after various types of tests.